wait kind of amp is it. you could always bridge it if the amp is able too. Yes you can only run one channel of the amp as long as it is able to take the ohms you are putting to it. example your amp is 2ohm stable and u try running it at 1ohm.

the amp is a fasgate 1000a2...2 ohm stable..i currently have it bridged and its way to powerfull for the sub...but if it is just drawing off of the left or right channel alone it would be pulling RMS power...i just didnt know if this would be safe on the amp

It is not recommended to run only one channel of a two channel amp. The reson being, the outoput transistors of most amps require a balanced load across both channels. I too would suggest turning the gain down to a level that works for your application.